1. Field of the Invention
The present invention relates to a fluorine-containing copolymer and a composition containing tha same, and more particularly to a novel fluorine-containing copolymer and a composition containing the same, the, composition being capable of producing a vulcanization product having a low compression set.
2. Description of the Prior Art
Copolymers of tetrafluoroethylene and perfluoro(methylvinylether) are completely fluorinated and thus have a good resistance to chemicals, whereas it is necessary to introduce a compound capable of forming a peroxide-vulcanizable, cross-linkable site in the copolymers because the copolymers have no cross-linkable sites. The compound capable of forming a peroxide-vulcanizable, cross-linkable site includes, for example, an iodine-containing compound, a bromine-containing compound, a cyano group-containing unsaturated compound, a phenoxy group-containing unsaturated compound,. etc.
JP-A-80-44511 discloses that tetrafluoroethyleneperfluoro(methylvinylgther) copolymers can have considerably improved cross-lining characteristics and: compression set characteristics by further copolymerizing a monomer having a cross-linkable site, represented by the general formula R.sub.1 CH.dbd.CR.sub.2 R.sub.3, wherein R.sub.1 and R.sub.2 are a hydrogen atom or a fluorine atom and R.sub.3 is a hydrogen atom, a fluorine atom, an alkyl group or a perfluoroalkyl group, for example, CH.sub.2 .dbd.CH.sub.2, CH.sub.2 .dbd.CHF, CH.sub.2 .dbd.CF.sub.2, CHF.dbd.CF.sub.2, CH.sub.2 .dbd.CHCF.sub.3, CH.sub.2 .dbd.CHC.sub.4 F.sub.9, etc., preferably trifluoroethylene or vinylidene fluoride, into the copolymers and by vulcanizing the resulting copolymers with dipotassium salt of bisphenol AF, etc.
However, as a result of extensive studies, the present inventors have been found that even if trifluoroethylene, which has been regarded as a preferable monomer capable of forming a cross-linkable site, is further copolymerized into the tetrafluoroethylene-perfluoro(methylvinylether) copolymer, followed by vulcanization with dipotassium salt of bisphenol AF, the compression set characteristics of the resulting vulcanization products fail to reach a fully satisfactory level.